mndot traffic sign life expectancy report

7/26/2019 MnDOT Traffic Sign Life Expectancy Report

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To request this document in an alternative format call 651-366-4718or 1-800-657-3774(Greater

Minnesota) or email your request to [email protected]. Please request at least oneweek in advance.


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Technical Report Documentation Page1. Report No. 2. 3. Recipients Accession No.MN/RC 2014-20

4. Title and Subtitle 5. Report Date

Traffic Sign Life ExpectancyJune 2014

6.

7. Author(s) 8. Performing Organization Report No.Howard Preston, Kristin C. Atkins, Matthew Lebens, and

Maureen Jensen9. Performing Organization Name and Address 10. Project/Task/Work Unit No.

CH2M HILL

1295 Northland Drive, Suite 200

Mendota Heights, MN 55120

Minnesota Department of Transportation

Office of Materials and Road Research

1400 Gervais Avenue

Maplewood, MN 55109

11. Contract (C) or Grant (G) No.

(C) 02889

12. Sponsoring Organization Name and Address 13. Type of Report and Period CoveredMinnesota Department of TransportationResearch Services & Library

395 John Ireland Boulevard, MS 330

St. Paul, MN 55155

Final Report14. Sponsoring Agency Code

15. Supplementary Noteshttp://www.lrrb.org/pdf/201420.pdf16. Abstract (Limit: 250 words)

Highway agencies with an inventory of traffic signs must adopt a method of maintaining those signs so that the

retroreflectivity exceeds established thresholds. Understanding expected sign life can help agencies phase sign

replacements over a number of years in order to manage maintenance costs. The primary goal of this research is toprovide objective data about sign life based on the degradation of retroreflectivity and color over time. A literature

review found sign retroreflectivity research around the country, however, none of the studies are conclusive. Eight

Minnesota agencies took retroreflectometer readings on in-place signs across the state. Disaggregated

measurements by sheeting material and color did not leave a large enough sample for conclusive results, and very

few signs fell below minimum retroreflectivity thresholds. Data suggests sign life exceeds the manufacturers

warranty and that a controlled environment with known conditions will produce more reliable data. MnDOT

established a test deck at MnROAD to take multiple retroreflectivity and color readings over time to the point of

failure in a controlled environment. The best information inferred from the results is an estimate for an expected

sign life of 12 to 20 years for beaded sheeting and 15 to 30 years for prismatic sheeting. Agencies are encouraged

to move forward and adopt a sign maintenance method and expected sign life by bringing sign management

decisions under an umbrella of immunity. This document has suggested best policy practices and statements for

sign maintenance and management assembled by a panel including engineers and risk management specialists.17. Document Analysis/Descriptors 18. Availability StatementSign sheeting, retroreflectivity, best practices, testing

equipment, maintenance management.

No restrictions. Document available from:

National Technical Information Services,

Alexandria, VA 22312

19. Security Class (this report) 20. Security Class (this page) 21. No. of Pages 22. PriceUnclassified Unclassified 45


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Traffic Sign Life Expectancy

Prepared by:

Howard Preston

K.C. AtkinsMatthew Lebens

Maureen Jensen

CH2M HILL

1295 Northland Drive

Suite 200Mendota Heights, MN 55120

Minnesota Department of TransportationOffice of Materials and Road Research

1400 Gervais Avenue

Maplewood, MN 55109

June 2014

Published by:

Minnesota Department of TransportationResearch Services & Library

395 John Ireland Boulevard, MS 330

Saint Paul, MN 55155

This report represents the results of research conducted by the authors and does not necessarily represent

the views or policies of the Minnesota Department of Transportation or CH2M HILL. This report doesnot contain a standard or specified technique.

The authors, the Minnesota Department of Transportation and CH2M HILL do not endorse products ormanufacturers. Any trade or manufacturers names that may appear herein do so solely because they are

considered essential to this report.


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Acknowledgements

The authors extend a thank you to the following individuals that contributed to the completion ofthis report through the investment of their time, energy and the sharing of their wisdom.

Tim Plath, City of EaganKristi Sebastian, Dakota CountyChris Smith, League of Minnesota CitiesSteve Kubista, Chippewa CountyMark Vizecky, MnDOT State Aid to Local GovernmentsHeather Lott, MnDOT Office of Traffic, Safety and TechnologyDan Sauve, Clearwater CountyRandy Newton, City of Eden PrairieVic Lund, St. Louis CountyMark Ray, City of Golden ValleyLee Amundson, Lincoln County (Retired)

Brad Lechtenberg, MnDOT State Sign ShopTrisha Nelson, MnDOT Metro District Office of Traffic EngineeringJim McGraw, MnDOT Office of Materials and Road Research


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Table of Contents

CHAPTER 1.INTRODUCTION ...............................................................................................................1

CHAPTER 2. LITERATURE SEARCH ..................................................................................................... 2

2.1LITERATURE REVIEW .......................................................................................................................... 2

2.1.1 FHWA [2] .................................................................................................................................... 2

2.1.2 NCHRP [3] .................................................................................................................................. 2

2.1.3 Oregon [4] ................................................................................................................................... 2

2.1.4 Purdue [5] .................................................................................................................................... 3

2.1.5 North Carolina [6] ....................................................................................................................... 3

2.1.6 Vermont [7] .................................................................................................................................. 4

2.1.7 Texas [8] ...................................................................................................................................... 4

2.1.8 Indiana [9] ................................................................................................................................... 5

2.1.9 Utah [10] ..................................................................................................................................... 5

2.1.10 Louisiana [11] ........................................................................................................................... 6

2.1.11 Texas Transportation Institute [12] ........................................................................................... 62.2LITERATURE REVIEW CONCLUSIONS.................................................................................................. 7

CHAPTER 3.MINNESOTA DATA COLLECTION .............................................................................. 8

3.1LOCAL AGENCY DATA COLLECTION .................................................................................................. 8

3.1.1 ASTM Type I Sheeting ................................................................................................................ 10

3.1.2 ASTM Type IV Sheeting ............................................................................................................. 10

3.1.3 ASTM Type IX Sheeting ............................................................................................................. 12

3.1.4 ASTM Type XI Sheeting ............................................................................................................. 13

3.1.5 Agency Data Summary ............................................................................................................... 14

3.2MNROADSIGN TEST DECK ............................................................................................................. 15

3.3DATA CONCLUSIONS ......................................................................................................................... 17CHAPTER 4.CONCLUSIONS ............................................................................................................... 19

REFERENCES .......................................................................................................................................... 21

APPENDIX A. SIGN POLICY ISSUE


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List of Tables

Table 2.1 North Carolina Predicted Sign Life..4

Table 2.2 Texas Average Number of Signs Per Mile vs. Minnesota Average.....5

Table 2.3 Type I Sheeting Life Expectancy Research..6

Table 2.4 Type III Sheeting Life Expectancy Research...7

List of Figures

Figure 3.1 - MN MUTCD Minimum Maintained Retroreflectivity Levels Table 2A-3......9

Figure 3.2 - Type I Sheeting Retroreflectivity Results...10

Figure 3.3 - Type IV Sheeting Retroreflectivity Results....11

Figure 3.4 - Type IX Sheeting Retroreflectivity Results........12

Figure 3.5 - Type XI Sheeting Retroreflectivity Results...13/14

Figure 3.6 - MnROAD Sign Test Deck Location ..15

Figure 3.7 - MnROAD Sign Test Deck Layout..16

Figure 3.8 - MnDOT Sign Test Deck Racks..17


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Executive Summary

The genesis of this project involves the requirement in theMinnesota Manual on Uniform Traffic

Control Devices(MN MUTCD)that all highway agencies with an inventory of traffic signs must

adopt a method of maintaining those signs so that the retroreflectivity exceeds the established

thresholds. This requirement has an implementation date of June 13, 2014.

A key element of typical sign maintenance programs is an understanding of the expected life of

traffic signs, which helps agencies phase their sign replacements over a number of years.However, this data does not currently exist for the inventory of signs in Minnesota and is only

available on a limited national basis, especially for the newer prismatic sheeting material (ASTM

Type IX and Type XI) that has been in use for fewer than ten years. As a result, agencies arefaced with a dilemma use a value that is available, the sheeting manufacturers warranty

period, or to subjectively select another value. Both choices present some level of risk to the

agency, as well as maximizing investment and safety. The use of the warranty period likely

results in replacing signs that have not reached the end of their useful lives which drives

maintenance costs up. Subjectively selecting a value that is not in common practice couldincrease an agencys exposure to claims of negligence and not address sign legibility and safety.

As a result, the primary objective of this research is to provide objective data about expected sign

life based on the degradation of retroreflectivity and color over time. In the likelihood that a

statistically reliable set of data could not be assembled within the limited timeframe of thisproject, a secondary objective involved providing local agencies with a subjective, best

practice set of suggestions. This includes involving both the expected sign life and an approach

to incorporating an adopted sign life into a comprehensive sign maintenance program.

The approach to conducting this project consisted of four key parts:

Reviewing previously published research that focused on the deterioration of traffic signs

and provided estimates of sign life.

Obtaining measured retroreflectivity levels of in-place signs from participating localagencies around Minnesota.

Establishing a test deck of traffic signs at the Minnesota Department of Transportations(MnDOT) MnROAD facility and documenting retro-reflectivity levels over the shortterm duration of this project and then into the future.

Assembling an expert panel to discuss the documented objective data provided by the

participating local agencies and from the MnROAD test deck. From this and a risk

management perspective, identifying an expected sign life (or range of years) that could

be used by local agencies to more effectively manage their system of traffic signs.

The results of these tasks include the following:

Research Review (Chapter 2)

Eleven previously published research reports were found that focused on identifying theexpected life of traffic signs. The authors looked at between approximately 140 and 5,700 signs,

the vast majority of which were in-place (along the public road system) and consisted of either


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ASTM Type I or Type III beaded sheeting material. These reports contained four key lessons

learned:

Sign orientation and weather did NOT appear to play substantial roles in the deteriorationof sign retroreflectivity although south facing red signs did experience an increase in

variability of retroreflectivity readings. The failure rates of the observed signs were in the range of 1% to 8%, depending on the

age of the sign. One study also identified an overall 6% sign replacement rate, withapproximately equal portions attributed to retroreflectivity failure and vandalism.

Many of the studies developed regression equations that forecast the long termdeterioration of retroreflectivity. In virtually every case, the regression equations forecast

sign life far beyond the manufacturers warranty period. However, in each case theauthors warned of possible credibility issues with their efforts because of environmental

factors associated with the in-place sample of signs that they couldnt account for in the

equations, small sample sizes and unrealistic results (sign lives in excess of 100 years).

The final lesson is the most important and speaks to the credibility of the results. None of

the research continued collecting retroreflectivity readings long enough to observe failurefrom the perspective of actually watching retroreflectivity of a set of signs drop below theestablished thresholds in a controlled setting. A number of the authors concluded that

until that kind of research is conducted, any results regarding sign life will continue to be

estimates as opposed to definitive values.

Measured Retro-Reflectivity of In-Place Signs (Chapter 3)

Three cities, four counties and MnDOTs Metropolitan District used a retroreflectometer to

collect readings at in-place signs around the State. A total of 379 valid readings were recordedand analyzed and approximately 10% of the readings were rejected, primarily due to errors in

readings (zero readings on white sheeting, extraordinarily high readings on black sheeting or

signs with Type XI sheeting listed as more than 7 years old as this material was only introduced7 years ago). By the time data was disaggregated by sheeting material, color and age of sign, nodata set had more than the desired 100 readings and no individual sign had more than one

retroreflectivity reading.

This data was analyzed and regression equations were developed that attempted to predict the

long term life of the signs based on both color and type of sheeting material. These results were

similar to those documented in the literature basically sign lives greater than themanufacturers warranty with some unusual results (trend lines indicating improved

retroreflectivity over time or estimated lives greater than 100 years). These results suggest the

need to provide the same caution to readers about the credibility of the results, similar to those

contained in the previous research.

Measured Retro-Reflectivity of Test Deck (Chapter 3)

The project anticipated that the information in prior research and generated from retroreflectivityreadings of in-place signs in Minnesota might not be sufficient to determine, with a high degree

of certainty, the expected lives of signs. As a result, a third approach to establishing sign life was

included in this project installing a test deck of signs at MnDOTs MnROAD facility. The testdeck was set up in June 2013 and signs were oriented in a way to try and cause accelerated


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deterioration (both south facing vertical and at a 45 degree angle). Readings for both

retroreflectivity and color have been taken. The conclusion of this effort is that there simply have

neither been enough readings nor enough time lapsed to determine a definitive value for sign life.

The in-field retroreflectometer readings demonstrate similar findings to those in the literature,

however, after disaggregation; more readings need to be performed. Due to difficultiesidentifying types of sheeting material and other factors such as sign knock downs or vandalism

of in-field signs, the test deck will provide valuable information over the years. The key for the

test deck is that the history of the signs is known (exact age and type of material), it is in a

controlled environment and signs can continue to be measured until retroreflectivity failure todetermine a more accurate sign life expectancy.

These results suggest two key points for local agencies. First, from both a risk management andsign management perspective it is very important for agencies to develop and adopt a sign

maintenance method, including identification of expected sign life. However, there is no

definitive information currently available to assist agencies in determining an exact value for the

life of a sign. The best information that can be inferred from the results of previous testing is thatthe expected life is most certainly longer than the manufacturers warranty period, with a

reasonable estimate in the range of 12 to 20 years for beaded sheeting and 15 to 30 years for

prismatic sheeting.

Agencies are encouraged to move forward and adopt both a sign maintenance method (prior to

June 13, 2014) and an expected sign life using the best practices technique of bringing signmanagement decisions under an umbrella of immunity. In Minnesota, this is done by having

agencies sign management decisions based on policies adopted by their elected officials and the

results of engineering studies conducted by the agencys professional staff or qualifiedcontractors.

In order to help agencies with policy development, a panel including both engineers and riskmanagement specialists was assembled as part of this project. This group generated a best

practices list of suggested statements (Appendix A) that is a useful tool and could be included in

an agencys sign maintenance policy and address topics such as the adopted maintenance

method, selected type(s) of sheeting material, expected sign life, details about the agencys signmaintenance priorities and the types of signs that are considered candidates for removal.


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Beaded sheeting types. Printed with permission from Federal Highway Association to assist withidentifying sheeting type. Last Accessed May 2014.

http://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdf
http://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdfhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdfhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdf


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Prismatic sheeting types. Printed with permission from Federal Highway Association to assist withidentifying sheeting type. Last Accessed May 2014.

http://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdf
http://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdfhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdfhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/sign_visib/sheetguide/sheetguide2014.pdf


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1

Chapter 1. Introduction

This project was encouraged and supported by local highway agencies in Minnesota because ofthe lack of sufficient information about the life expectancy of traffic signs, primarily as afunction of the degradation of the level of retroreflectivity over time. The approach to providing

an answer to the question whats the expected life of a traffic sign consisted of four key parts:

Reviewing the literature documenting the results of previously published research.

Obtaining measured retroreflectivity information from local agencies in Minnesota.

Establishing a test deck of traffic signs at the Minnesota Department of Transportations(MnDOT) MnROAD facility and documenting the retroreflectivity over the short termduration of this project, and into the future.

Assembling an expert panel to discuss the documented objective data and then from the

perspective of risk management, identify a sign life expectancy (or range of years) thatcould be used by local agencies to more effectively manage their systems of traffic signs.

The primary information that currently provides insight about sign life expectancy is thewarranty period provided by manufacturers 7 years for ASTM Type I, 10 years for ASTMType IV, 12 years for ASTM Type IX and ASTM Type XI sheeting. The concerns expressed bymany local agencies is that warranty values are probably conservative and their use in a signmaintenance program could result in many signs being replaced with possibly many years ofeffective life left, which would ultimately drive up agencies annual sign maintenance costs. Thisconcern about assumptions regarding sign life unnecessarily increasing the costs of signmaintenance drove the local agencies in Minnesota to seek the most current and regionalinformation possible to help them make informed and cost-effective decisions about their signmaintenance programs, while remaining consistent with best practices for risk management.

The primary objective of this research is to provide objective data about sign life that is notcurrently available, especially for the newer, prismatic sheeting material (i.e., ASTM Type XIand IX) that has only been in use for fewer than ten years. In addition, in anticipation of thelikelihood that a statistically reliable sample of objective data couldnt be assembled, a secondaryobjective involved providing local agencies with a subjective, best practices set of suggestionsinvolving both the expected sign life and an approach to incorporating an adopted sign life into acomprehensive sign maintenance policy.


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2

Chapter 2. Literature Search

Prior to the addition of required minimum values of retroreflectivity to the MinnesotaManual onUniform Traffic Control Devices (MN MUTCD), sign maintenance was a recommended activityand highway agencies were left to determine how they would proceed [1]. Some agencies

conducted nighttime inspections and some used expected sign life to determine a replacementcycle. At that time, the only information available was the warranty period established by thesheeting manufacturers, which is based on factors other than meeting minimum retroreflectivity.However, as sign sheeting material improved and new sheeting was developed, theretroreflectivity became significantly higher than theMNMUTCDminimum. It is thereforereasonable to expect the service life of signs from these newer materials to be much longerbefore degrading to minimum required values. Because of the improvements to sign sheetingmaterials, sign retroreflectivity has been studied by multiple agencies with a focus ondetermining a realistic sign life for different sheeting materials.

2.1 Literature Review

The Federal Highway Administration (FHWA) and several states have conducted studies todetermine deterioration rates of sign sheeting. The majority of these studies have focused onType I and III sheeting materials, since that was what the majority of agencies had installed andwere available for a field aging study.

2.1.1 FHWA [2]

In 1992, FHWA conducted a national study to determine the factors that contribute toretroreflective degradation and to develop predictive models for Type III sheeting. Data wascollected on 5,722 signs in 18 different states across the country. The study found that there wassignificant variation in readings and that age, precipitation, elevation and temperature affecteddeterioration. It also showed that sign direction was not a factor in retroreflectivity deterioration.

Linear prediction models were developed, and showed that signs Type III performed adequatelyfor up to 12 years.

2.1.2 NCHRP [3]

The NCHRP Synthesis 431, Practices to Manage Traffic Sign Retroreflectivity, documentedthe state of practice agencies are using for maintaining sign retroreflectivity. The study foundthat most agencies report that the various sheeting materials outlast the warranty period and thatType I is the least efficient and shortest lasting sheeting material. Study participants noted that itis more cost-effective to install Type III or IV sheeting material than Type I.

2.1.3 Oregon [4]

In 2001, Oregon conducted a study to understand the drivers of retroreflectivity degradation toprovide guidance to the Oregon Department of Transportation (ODOT). Data was collecting on80 Type III (HI) signs that had been in service for 10 years. Red, yellow, green and white signdata was collected (20 signs each) and 10 readings were taken on each sign background. Theinitial data set of 80 signs was found to be insufficient, so an additional 57 signs were measuredto provide a more complete data set. The second data set had markedly higher readings than thefirst (71% to 107%). Between the two sets of readings, the meter used was calibrated at thefactory, possibly accounting for the difference in readings. Thus, a weighting factor derived from


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the average percentage difference of the second round readings compared to the first was appliedto the first round of data. The average of the 10 readings per sign was used to represent theoverall sign retroreflectivity due to the variability in the reflective surface.

Linear trend lines applied to the data showed little relationship between the age of signs and their

retroreflectivity values. It was determined that there may not have been a great enough age range(12 years) of signs to provide a complete picture of the retroreflectivity performance over timeand any weathering effects.

The study showed that over a twelve year span most signs exceeded the minimum standard. Thestudy found some indications that retroreflectivity may be affected by sign orientation due toweathering effects of windblown dust and precipitation, but there was no strong trend in the datato support this. It was noted that west-facing signs resulted in lower retroreflectivity readings forwhite, yellow and green signs, while south-facing signs resulted in lower retroreflectivityreadings for red signs. However, the variability in the average levels of retroreflectivity is not asevident.

2.1.4 Purdue [5]

In 2002, Purdue University conducted a study for the Indiana DOT on their Type III signs.Retroreflectivity on 1,341 in-service Type III red, white and yellow sign backgrounds weremeasured across Indiana. Sign types included, but were not limited to STOP, DO NOT ENTER,WRONG WAY, No Passing and route markers. Conclusions from the study were:

Retroreflectometer readings varied depending upon which measuring instrument wasused and raises concerns regarding state liability.

There was no real link between age and retroreflectivity readings of white and yellowsigns.

There was a more apparent downward trend in the retroreflectivity of red signs as thesigns age. This trend was not considered very strong as there was only a 33 percentcorrelation between age and average retroreflectivity of the sign.

Orientation did not play a major role in sign deterioration.

The majority (98%) of signs that had white and yellow backgrounds kept retroreflectivity

levels above the proposed minimums out past 15 years of age.

The overall study concluded that due to the long lasting nature of signs it is possible that thewhite and yellow type III signs could be left out in the field longer than they currently are andcould save INDOT money in life cycle costs. The study recommended that for white and yellowbackground signs, service life could be safely extended to 12 years. The study recommended that

red sign service life remain at the 10 year warranty not because of retroreflectivity, but due tocolor fade.

2.1.5 North Carolina [6]

North Carolina State University conducted a study for the North Carolina Department ofTransportation (NCDOT) in 2005 and 2006, where they evaluated the DOTs nighttimeinspection process, determined sign retroreflectivity expected life, and determined factors thataffect sign performance. The field study sign damage rate was 2.37% of the inspected signs per


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year with 1.3% damaged by humans, 0.9% by natural causes and 0.17% by humans and naturalcauses. The most common causes of damage were paint balls, gun shots, eggs and tree sap. In asecond investigation, the researchers found that 4.7 % of signs are replaced due to damage eachyear and includes 2.4 % of signs replaced outside the nighttime inspection process due tovandalism. Based on this, an overall sign replacement rate of 6.9% was determined.

Retroreflectivity was measured on 1,047 Type I and III in service signs and compared the resultsto field inspectors night-time visual assessments. A linear trend line was found to be the best fitfor the retroreflectivity degradation over time. The study determined that signs would reach zeroretroreflectivity after 20 to 30 years. Table 2.1 demonstrates the determined sign life from thestudy based on the best fit linear trend lines.

Table 2.1 North Carolina Predicted Sign Life

Sign Color Type I Sign Life Type III Sign Life

White 24-45 67- >80

Yellow 26-31 42- >80Red 21-24 22-42

Green 29 30

In addition to sign life, the study determined a visual inspection cost of $0.55/sign. Forcomparison, a typical Minnesota county has 10,000 signs and the annual visual inspection costwould be $5,500 per year. Inspection cost using a retroreflectometer was determined to be $2.80per sign, which would cost a Minnesota county $28,000 per year to inspect all of the agencyssigns. Accuracy of the nighttime visual inspectors of the North Carolina study compared toretroreflectometer readings varied from 54% to 83%.

2.1.6 Vermont [7]

In 2008 the Vermont Transportation Agency measured retroreflectivity of 398 Type III signs in

green, red, yellow and white. Two-hundred twenty yellow and yellow-green Type IX signs thathad been in service for 6 years were also measured. The study found no significant correlation toorientation or offset, though north facing signs had higher retroreflectivity than south facing. Thestudy also found that red sign retroreflectivity deteriorated faster than other sign colors, whilewhite deteriorates the slowest. Type III sign life based on trend lines ranged from 15 (red) toover 9,000 (green) years. The researchers mentioned that the extremely high sign life isunreasonable and likely due to limited long term data. Type IX sign life expectancy was 95 yearsfor both yellow and yellow-green. Based on this study, Vermont adopted a 15 year life for allsign colors, retroreflectivity measurements of signs will continue as no signs were found to bebelow the minimum retroreflectivity requirements.

2.1.7 Texas [8]In 2009 Texas A&M measured retroreflectivity of 1,385 Type I, III and prismatic red, white,green and yellow signs for the Texas DOT to identify compliance rates. Overall, 70 signs failedto meet minimum retroreflectivity requirements, including 2 prismatic signs, which wereconsidered outliers resulting from accelerated environmental deterioration. The study found thatsign direction was not a factor in retroreflectivity and that daytime visual assessments are NOT agood indicator for retroreflectivity. Regional variations were also not significant to warrantdifferent sign management practices for different regions. Sign life expectancy is important to


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5

the Texas DOT due to the number of signs on its system, similar to Minnesota concerns. Table2.2 demonstrates the comparison of signs per mile on each roadway system.

Table 2.2 Texas Average Number of Signs Per Mile vs. Minnesota Average

Location Freeway Arterial Collector Local

Overall

TXAverage

Overall

MNCounties

Average

Rural 9 13 11 714 10

Urban 13 25 30 8

Based on linear regression, many of the signs in the various regions had service lives rangingfrom 15 to 155 years. The study found that the failure rate for Type III signs 10-12 years of agewas 2 percent and 8 percent for signs 12-15 years. Researchers also conducted a long termaccelerated weathering study on Types I through IX that showed color fading is a significantissue. Projected sign life ranged from 15 to 155 years and the trends are similar to those

completed in other studies.

The study also reviewed a mobile data collection technology that takes readings from a vehicle.It was found that this system failed to accurately measure sign retroreflectivity and could resultin waste to agencies removing signs that are still meeting minimum retroreflectivityrequirements. The study ultimately concluded that none of the management and maintenancepractices identified and in use in Texas meet FHWA intent for conducting nighttime visualinspections, despite the processes being documented across the state.

2.1.8 Indiana [9]

Indiana DOT conducted an evaluation in 2010-11 for their sign sheeting materials. Up to that

point, Indiana had been using a 14 year service life. Researchers performed measurements on211 signs facing different directions from northern and southern Indiana. Most of the signs wereType III (some Type I) with one group of Type IV that was 10 to 11 years old. All but 11 signs(approximately 5 percent) were above theMNMUTCDminimum, and several of these seemedto be damaged. The Type IV sign readings were significantly higher than minimumretroreflectivity requirements.

Researchers also measured color and found that all the green signs were within the colorspecification limits. The majority of the white and yellow were also within specifications, but thered signs, including the 10 year old Type IV signs failed to meet specifications. Indiana DOTadopted an 18 year life for sheet signs and 20 year life for panel signs.

2.1.9 Utah [10]

In 2011 and 2012, Utah State University conducted a study for the Utah DOT and collectedretroreflectivity data on 1,716 signs. By the end of the study, 28 percent of the signs weresignificantly damaged, while 7 percent did not meet minimum retroreflectivity levels. Damagewas categorized into aging (cracking or peeling), environmental (wind, snow, vehicle knockdowns or tree sap) and vandalism (paintballs, bullet holes, eggs, bumper stickers and spraypaint). Overall, only 1% of signs would have needed replacement that would not have already


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6

been replaced due to damage (6% of damaged signs did not meet minimum retroreflectivityrequirements). This is consistent with the FHWA study that found rural areas can have highincidence of damage.

2.1.10 Louisiana [11]

In 2005, the Louisiana Department of Transportation (LADOT) collected sign retroreflectivitydata to predict the sign performance. They used expected sign life for their management method,and evaluated data measurements on 237 signs (Type I and III, white, green and yellow).Overall, 92% of the signs still covered under warranty were above the minimum retroreflectivityrequirements. Signs outside of the warranty had 43% at or above minimum retroreflectivity. Thestudy noted the benefits of cleaning signs and that retroreflectivity levels increased when signswere cleaned. After this study, the LADOT adopted a 25 year service life for prismatic and 20year life for all beaded sheeting, which took into account other national studies and research.

2.1.11 Texas Transportation Institute [12]

Bradford Brimley and Paul Carlson from Texas Transportation Institute (TTI) presented their

latest work at the 2013 Transportation Research Board (TRB) annual meeting from their paperThe Current State of Research on the Long-Term Deterioration of Traffic Signs [12]. Theyreviewed some of the projects listed above along with others and summarized the expected yearsto failure of each study. Table 2.3 summarizes Type I sign sheeting life expectancy and Table 2.4summarizes Type III sign life expectancy.

The TTI review noted that Vermont was the only source of information for Type IX sheetingdata and based on only 6 years of data. The authors concluded that the data did not producereasonable predictions (more than 70 years) to failure. The researchers also discussed theproblems with bias in field studies that drop early failures (due to replacements), haveunbalanced numbers of signs, in addition to the problems of wide scatter in the data fromunknown causes.

From a previous study by Brimley, Hawkins and Carlson titled Analysis of Retroreflectivity andColor Degradation in Sign Sheeting, [13], results from an experiment of 9 different sheetingproducts were weathered on an outdoor 45 degree rack for 10 plus years, (or a simulated 21 yearsof service based on an assumption of twice the normal rate of degradation when installed at 45degrees) were discussed. Most of the sheeting met retroreflectivity requirements over a 15 yearsimulated life, but some fell outside of the color (fade) specifications in less than five simulatedyears. Overall the authors found that products failed due to color fade loss of beforeretroreflectivity. As color fades, retroreflectivity can increase initially, complicating the analysis.The study also noted that this study included only one sample of each sheeting type and color.

Table 2.3 Type I Sheeting Life Expectancy Research

Color Number of

Studies

Publication

Years

Sample Sizes Years to Failure

(2009 MUTCD)

White 5 1990-2006 40-1,084 6-13Yellow 5 1990-2006 42-931 Not Permitted

Red 2 1991-2006 50-697 9-16Green 5 1990-2006 42-704 10-16


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Table 2.4 Type III Sheeting Life Expectancy Research

Color Number of

Studies

Publication

Years

Sample Sizes Years to Failure

(2009 MUTCD)

White 8 1990-2012 35-909 34-740

Yellow 7 1991-2012 32-409 17-53

Red 6 1990-2012 84-662 15-NeverGreen 5 1991-2009 46-326 9-740

2.2 Literature Review Conclusions

Eleven different sign retroreflectivity research documents were reviewed. Overall, each studylooked at between approximately 140 and 5,700 signs, the vast majority of which were in-place(along the public road system) and consisted of either ASTM Type I or Type II sheetingmaterial. The literature review resulted in four key conclusions as follows:

Sign orientation and weather did NOT appear to play substantial roles in the deteriorationof sign retroreflectivity although south facing red signs did experience an increase in

variability. Daytime inspections were NOT as good as nighttime inspections for identifying signs

that fail via retroreflectivity or color fade.

The failure rates of the observed signs were in the range of 1% to 8%, depending on the

age of the sign. One study also identified an overall 6% sign replacement rate, withapproximately equal portions attributed to retroreflectivity failure and vandalism.

Linear regression equations were the best fit in most studies for forecastingretroreflectivity degradation.

Many of the studies developed regression equations that forecast the long termdeterioration of retroreflectivity. In virtually every case, the regression equations forecastsign life far beyond the manufacturers warranty period. However, in each case the

authors warned of possible credibility issues with their efforts because of environmentalfactors associated with the in-place sample of signs that they couldnt account for in theequations, small sample sizes and unrealistic results (predicted sign lives in excess of 100years).

Color fade may be as large of an issue or cause for failure as retroreflectivity degradation.

The final lesson is the most important and speaks to the credibility of the results. None ofthe research continued collecting retroreflectivity readings long enough to observe failurefrom the perspective of actually watching retroreflectivity of a set of signs drop below theestablished thresholds in a controlled setting. A number of the authors concluded thatuntil that kind of research is conducted, any results regarding sign life will continue to beestimates as opposed to definitive values.


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Chapter 3. Minnesota Data Collection

At the outset of the approach to acquiring readings of retroreflectivity through local Minnesotaagencies, it was determined that the ideal number of signs necessary to produce statisticallycredible results would be one-hundred. In addition, to precisely determine sign life would

require being able to observe the same signs over a long enough span of years for observedlevels of retroreflectivity to drop below the established minimum thresholds. A sign test deckwas established in order to observe individual signs fabricated with the newest sheeting materialsover many years to better understand sign retroreflectivity degradation.

3.1 Local Agency Data Collection

Project staff worked with seven local agencies and the MnDOT research lab to collectretroreflectivity data on existing signs in the field. Data collection focused on 4 ASTM sheetingtypes, Type I, IV, IX and XI with green, red, white or yellow backgrounds. Readings weremostly taken from south facing signs, as these signs are subject to the most sunlight year-roundand have been observed in previous studies to degrade faster that signs facing other directions.

Existing sign inventories from each agency were used to determine the age of the sign.

Three-hundred seventy-nine valid readings were recorded by the City of Eagan, City of GoldenValley, City of Brooklyn, Dakota County, St. Louis County, Watonwan County, MnDOTResearch and the MnDOT Metro District using a MnDOT provided retroreflectometer.Approximately ten percent of the initial data was removed or modified due to one of thefollowing:

1) Data was corrected or removed if it was evident the background and legend had beenaccidentally misidentified during the data recording process.

2) Readings of zero on white sheeting and high readings on black were removed, possibly

due to the instrument being improperly placed on the sign.3) Signs listed as more than 7 years old and identified as Type XI sheeting were removed asthe material was introduced 7 years ago.

By the time data was disaggregated by sheeting material, color and age of sign, no sign data sethad more than 100 sign retroreflectivity readings. In addition, a limitation of the data is that nosign had more than one individual retroreflectometer reading, preventing that particular signsretroreflectivity to be measured over time. Therefore, each sign only has a single data pointassociated with it. Only background color retroreflectivity data was analyzed due to the increasederror potential in the smaller and narrower legend text. The data was graphed in MicrosoftExceland linear trend lines were added to the data points to estimate sign life expectancy with

regards to retroreflectivity failure. These trend lines were then compared to the minimumretroreflectivity requirements from theMN MUTCD(Figure 3.1).


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Figure 3.1 - MN MUTCD Minimum Maintained Retroreflectivity Levels Table 2A-3 [1]


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3.1.1 ASTM Type I Sheeting

Data was collected on 17 red signs and 23 yellow signs with Type I sheeting. Red sign data wascollected on signs of two ages (11 and 15 years) and yellow on signs of 4 ages (11, 15, 17 and 21years). While none of the signs fell below the minimum retroreflectivity levels, both trend linesslope upward and are therefore inconclusive due to insufficient data or the affects of color fade.

It should also be noted that theMN MUTCDnow states that Type I sheeting should not be usedfor black on yellow signs. Figure 3.2 demonstrates the results of the Type I retroreflectometerreadings.

3.1.2 ASTM Type IV Sheeting

Data was collected on 5 green signs, 9 red signs, 14 white signs and 11 yellow signs with TypeIV sheeting. Green sign data was collected on signs of 4 ages (13, 19, 21 and 22 years), redcollected on signs of 5 ages (7, 11, 15, 19 and 22 years), white on signs of 9 ages (7, 9, 13, 15,

17, 19, 20, 22 and 23 years) and yellow on signs of 10 ages (2, 7, 12, 13, 14, 15, 16, 17, 19 and24 years). Only 2 signs fell below the minimum retroreflectivity levels, one white sign (13 years)that would not meet overhead minimum values for legend on green signs and one yellow sign(24 years) that would not meet any minimum levels. Green Type IV trend line data slopedupward and was inconclusive. Red, white and yellow sign data trended downward, crossingminimum retroreflectivity levels between 23 and 82.5 years. However, due to low number ofdata points, the trend lines are considered inconclusive. Figure 3.3 demonstrates the results of theType IV sheeting retroreflectometer readings.

Figure 3.2 Type I Sheeting Retroreflectivity Results


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Figure 3.3 Type IV Sheeting Retroreflectivity Results


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3.1.3 ASTM Type IX Sheeting

Data was collected on 14 red signs, 5 white signs and 11 yellow signs with Type IX sheeting.Red sign data was collected on signs of 8 ages (3, 4, 9, 12, 14, 16, 17 and 24 years), white signdata was collected on 4 ages (4, 8, 9 and 10 years) and yellow on signs of 6 ages (4, 7, 9, 11, 13and 14 years). No signs fell below the minimum retroreflectivity levels. White Type IX trend

line data sloped upward and was inconclusive. Red and yellow sign data trended downward,crossing minimum retroreflectivity levels between 27 and 50 years. However, the data for allcolors is also considered inconclusive due to an insufficient amount of sign data. Figure 3.4demonstrates the results of the Type IX sheeting retroreflectometer readings.

Figure 3.4 Type IX Sheeting Retroreflectivity Results


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3.1.4 ASTM Type XI Sheeting

Data was collected on 35 green signs, 78 red signs, 91 white signs and 65 yellow signs with TypeXI sheeting. Green sign data was collected on signs of 7 ages (New, 1, 3, 4, 5, 6 and 7 years), redwas collected on signs of 7 ages (New, 2, 3, 4, 5, 6 and 7 years), white on signs of 8 ages (New,1, 2, 3, 4, 5, 6 and 7 years) and yellow on signs of 7 ages (New, 1, 2, 4, 5, 6 and 7 years). No

signs fell below the minimum retroreflectivity levels. Green Type XI trend line data slopedupward and was inconclusive. Red, white and yellow sign data trended downward, crossingminimum retroreflectivity levels between 36 and 133 years. However, due to insufficient data, allsign color trend lines are considered inconclusive. Figure 3.5 demonstrates the results of theType XI sheeting retroreflectometer readings.

Figure 3.5 Type XI Sheeting Retroreflectivity Results


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Figure 3.5 (Continued) Type XI Sheeting Retroreflectivity Results

3.1.5 Agency Data Summary

While most trend lines for the different sheeting types are in the downward direction andindicates a sign life greater than the warranty periods, there was not enough data (less than 100signs per data set) once the information was disaggregated by sheeting type and color foranalysis to come to a definite sign life conclusion. In addition, only a handful of signs fell belowthe minimum retroreflectivity requirements. Toward the end of this study, after retroreflectivityreadings were analyzed, a few agencies noted that sign types had been misidentified in theoriginal readings. This further reinforces a need for retroreflectivity readings on signs in acontrolled environment, over a long period of time to the point of failure.

While the data is inconclusive, it does seem feasible to suggest a range for sign life that can bereevaluated as more data is collected from the test deck for more conclusive results. Initial trendlines suggest a sign life of 12 to 20 years for beaded sheeting and 15 to 30 years for prismaticsheeting could be a reasonable sign life expectation for Type I, IV, IX and XI sheeting materialof all colors, but further study and data is needed. It is important to reevaluate this sign life rangeas more data is available. It should be noted that color degradation can result in an initial increasein retroreflectivity. More research is required to clarify the relationship.


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3.2 MnROAD Sign Test Deck

MnDOT planned to install a sign test deck at the outset of this project because of a concern thatthe retroreflectivity readings of in-place signs may not provide the desired high level of statisticalreliability. The results of the agency retroreflectometer readings were determined to beinconclusive and this reinforces the need for the test deck and testing both retroreflectivity and

color degradation of different sheeting materials and colors over the course of time, in acontrolled environment. A controlled environment ensures correct sign sheeting identificationand sign knock downs, vandalism or other outside factors will not interfere with data collection.Signs will ideally be tracked to the point of failure in order to develop a more conclusive trendline for sign life.

A traffic sign test deck was established in June 2013 at MnDOTs MnROAD site nearAlbertville, MN. Figures 3.6 and 3.7 show the test deck location at the MnROAD facility and theas-built layout of seven sign racks with the different sheeting materials facing four cardinaldirections. The majority (4) of the sign racks are south facing since other studies have shownsouth facing signs are typically the first for retroreflectivity to degrade (though not significantly

faster than other directions) as they are exposed to the sun for longer periods throughout the year.In addition, other studies have found that some colors, red in particular, fade faster on southfacing signs.

Figure 3.6 - MnROAD Sign Test Deck Location


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Figure 3.7 - MnROAD Sign Test Deck Layout

One of the south facing sign racks is placed at a 45 degree angle to simulate speeding the

degradation process by approximately twice as much as a vertical sign. This sign rack willprovide sign life results sooner than the vertical racks for agencies to use for sign replacementthat will eventually be supported by data from the vertical sign racks. Figure 3.8 shows the signtest deck in place at MnROAD in July 2013 with the initial Type XI test panels installed.


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Figure 3.8 - MnDOT Sign Test Deck Racks

Retroreflectivity and color (color is being collected to see if it falls below minimum thresholdsprior to retroreflectivity, which could affect sign life expectancy) data will be collected overmultiple years from the MnDOT sign test deck in order to obtain more data points, repeatedretroreflectivity readings on the same sign panels, and to better determine an actual sign life forsigns in a Minnesota climate.

3.3 Data Conclusions

Based on the collected data and data evaluated during the literature review, key conclusionsinclude:

There is not enough Minnesota retroreflectivity data (in-place and on the test deck) as of

the end of 2013 to establish a statistically reliable data set that would allow thedetermination of an exact value for sign life. After signs were disaggregated by sheetingmaterial and sign color, there were too few overall numbers of signs, no repeated testingof the same signs, misidentified sheeting materials and virtually no signs observed tofailure at this time.

Vandalism and knock-downs effect sign life at different rates in different agencies, butare a key factor in expected sign life spans.

The data suggest a reasonable estimation of sign life in the range of 12 to 20 years for

ASTM Type I and IV sheeting material.

The data suggest a reasonable estimation of sign life in the range of 15 to 30 years forASTM Type IX and XI sheeting material.

Color (especially for red signs) may fall below adopted thresholds (contrast/fade) prior toretroreflectivity failure.

Continued data collection is planned at the MnROAD test deck and will be reevaluated inthe future in order to observe signs in a controlled setting until they fail.

There is not sufficient local retroreflectivity data to definitely establish sign life with a highdegree of statistical reliability. As a result, the subjective risk management approach, involving


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suggestions from an expert panel to help establish a best practices approach for local agenciesuse in establishing their sign maintenance programs is recommended.

The MnROAD test deck will provide valuable results over time with continued retroreflectivityand color readings to failure in a controlled environment. Agencies may also continue to check in

on the MnROAD sign test deck to see if retroreflectivity or color readings and trendlines aremore statistically reliable and indicating a different sign life than their sign maintenanceprograms. Ideally, data collection will occur on the test deck until sign failure to determine amore narrow range, or definitive sign life.


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Chapter 4. Conclusions

Sign life is a topic of interest across the spectrum of Government agencies in Minnesota becauseit is a key part of developing a comprehensive sign maintenance program, which all agencies arerequired to have in place by June 13, 2014.

A review of eleven published research articles indicates that a variety of analyses have beenstarted but none of the results are considered definitive for Minnesota due to a variety of reasons,including:

Most of the studies are on Type I or III signs with limited data on newer sheeting types.

Authors frequently warned of possible credibility issues with data due to a variety ofissues including environmental factors, small sample sizes and unrealistic results(projected sign lives in excess of 100 years) that could not be accounted for.

Daytime inspections are NOT as good as nighttime inspections for identifying failures orretroreflectivity or color fade.

Retroreflectivity failure rates of signs were observed in the range of 1% to 8%. Tests were performed in different climates than Minnesota.

Many studies brought forth concerns regarding limited information about the actual signhistories.

None of the research collected retroreflectivity readings long enough to observe failure ofin-place signs, while other test decks have not been in-place long enough for newersheeting material to approach adopted retroreflectivity thresholds.

Retroreflectivity data collected on in-place signs from eight Minnesota agencies resulted inexpected sign life trendlines similar to those of published research. However, none of these signshave been in-place long enough to observe failure and factors such as knock-downs, vandalism

and sign sheeting misidentification make it difficult to collect reliable retroreflectivity data onthe same signs over a period of time, making it difficult to narrow in on a definitive expectedsign life. Minnesota data and previous research suggests a definitive sign life determinationwould require observing a test deck in a controlled environment and observing retroreflectivityto failure below established thresholds.

The test deck of signs installed by MnDOT at the MnROAD facility should add valuableinformation to the discussion of sign life, but not until several years in the future as multipleretroreflectivity readings are taken on the same signs with known information and noenvironmental factors affect the signs. These signs have not been in-place long enough to eitherhave enough readings to be considered statistically credible at this time or to establish trend lines

that are reliable. However, MnDOT has committed to continue collecting both retroreflectivityand color data on the MnROAD test deck, to a point of failure to better determine a definitiveexpected sign life.

Initial data from agency readings of in-place signs and the MnROAD test deck suggests areasonable sign life expectancy of 12 to 20 years for beaded sheeting and 15 to 30 years forprismatic sheeting. These values will continue to be updated and reviewed as more informationis available from the MnROAD test deck to determine a definitive expected sign life.


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In the near future, these results suggest two key points for agencies. First, from both a riskmanagement and sign management perspective it is very important for agencies to develop andadopt a sign management method, including the identification of expected sign life. However,there is no definitive information currently available to assist the agencies in determining a sign

life. As a result, agencies are encouraged to move forward using the best practices technique ofbringing sign management decisions under an umbrella of immunity by having sign managementdecisions based on policies adopted by their elected officials and the results of engineeringstudies conducted by the Agencys professional staff or qualified consultant.


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REFERENCES

1.

Minnesota Department of Transportation (MnDOT).Minnesota Manual on Uniform TrafficControl Devices. MnDOT, St. Paul, MN, January 2014.

2.

Black, K.L., H.W. McGee, S.F. Hussain, and J.J. Rennilson. Service Life of Retroreflective Signs.Report No. FHWA-RD-90-101. U.S. Department of Transportation, Federal HighwayAdministration, Washington, D.C. 1991.

3.

R, J.M., Carlson, P.J.NCHRP Synthesis 431: Practices to Manage Traffic Sign Retroreflectivity.Transportation Research Board of the National Academies, Washington, D.C., 2012.

4.

Kirk, A.R., Hunt, E.A., and Brooks E.W. Factors Affecting Sign Retroreflectivity. PublicationOR-RD-01-09. Oregon Department of Transportation, Salem, Oregon. 2001. Last accessed April2014.http://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/FactorsAffectSignRetroreflectivity.pdf

5.

Bischoff, A. and D. Bullock. Sign Retroreflectivity Study. Report No. FHWA/IN/JTRP-2002/22.Indiana Department of Transportation, Indianapolis, IN, December 2002. Last accessed April2014. http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1661&context=jtrp

6.

Rasdorf, W.J., J.E. Hummer, E.A. Harris, V.P.K. Immaneni, and C. Yeom.Designing an EfficientNighttime Sign Inspection Procedure to Ensure Motorist Safety. Report FHWA/NC/2006-08.North Carolina Department of Transportation, Raleigh, North Carolina, 2006. Last accessed April2014.http://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdf

7.

Kipp, W.M.E. and J.M.V. Fitch.Evaluation of Measuring Methods for Traffic SignRetroreflectivity. Publication 2009-8. Vermont Agency of Transportation, Montpelier, Vermont,2009. Last accessed April 2014.

http://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdf

8.

Carlson, P.J., L. Higgins, and J. R.Research and Recommendations for a Statewide SignRetroreflectivity Maintenance Program. Report FHWA/TX-12/0-6408-1. Texas Department ofTransportation, Austin, Texas, 2011. Last accessed April 2014.http://ntl.bts.gov/lib/44000/44500/44591/0-6408-1.pdf

9.

Nahrwold, T., Field Inspections for Sheet Sign Life Cycle Study Report.Indiana Department ofTransportation. Unpublished report.

10.

Boggs, W., Heaslip, K., and Louisell, C.Analysis of Sign Damage and Failure: A Case Study inUtah. Transportation Research Board of the National Academies, Washington D.C., 2013

11.

Wolshon, B., R. Degeyter, and J. Swargam.Analysis and Predictive Modeling of Road SignRetroreflectivity Performance.16th Biennial Symposium on Visibility and Simulation. Iowa City,Iowa, 2002.
http://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/FactorsAffectSignRetroreflectivity.pdfhttp://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/FactorsAffectSignRetroreflectivity.pdfhttp://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1661&context=jtrphttp://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1661&context=jtrphttp://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdfhttp://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdfhttp://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdfhttp://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdfhttp://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdfhttp://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdfhttp://ntl.bts.gov/lib/44000/44500/44591/0-6408-1.pdfhttp://ntl.bts.gov/lib/44000/44500/44591/0-6408-1.pdfhttp://ntl.bts.gov/lib/44000/44500/44591/0-6408-1.pdfhttp://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdfhttp://vtransengineering.vermont.gov/sites/aot_program_development/files/documents/materialsandresearch/completedprojects/SS_RR_Final_Report_Web_Version_1.pdfhttp://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdfhttp://www4.ncsu.edu/~eagrafpe/Designing%20an%20Efficient%20Nighttime%20Inspection%20Procedure%20to%20Ensure%20Motorist%20Safety.pdfhttp://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1661&context=jtrphttp://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/FactorsAffectSignRetroreflectivity.pdf


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12.

Brimley, B., Carlson, P. The Current State of Research on the Long-term Deterioration of TrafficSigns. Paper No. 13-0033. Transportation Research Board of the National Academies,Washington D.C., 2013. Last accessed April 2014.http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/TRB-130033.pdf

13.

Brimley, B., Hawkins, H.G., and Carlson, P.Analysis of Retroreflectivity and Color Degradation

in Sign Sheeting. Paper No. 11-2148. Transportation Research Board of the National Academies,Washington D.C., 2011. Last accessed April 2014.http://amonline.trb.org/12kebs/12kebs/1

14.

Federal Highway Administration.Manual on Uniform Traffic Control Devices. FHWA,Washington, D.C., 2009.

15.

Federal Highway Administration. Sign Retroreflectivity Toolkit New National Standard.Publication No. FHWA-CFL/TD-09-005. Washington D.C. Last accessed May 2014.http://safety.fhwa.dot.gov/roadway_dept/night_visib/retrotoolkit/index.htm

16.

TKDA.Evaluation of MnDOTs Sign Replacement Method. Project No. 15310.000. MnDOT, St.Paul, MN, 2013.

17.

Preston, H. and Barry, M.Minnesotas Best Practices for Traffic Sign Maintenance/ManagementHandbook. Report No. 2010RIC10. MnDOT, St. Paul, MN, 2010.

22
http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/TRB-130033.pdfhttp://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/TRB-130033.pdfhttp://amonline.trb.org/12kebs/12kebs/1http://amonline.trb.org/12kebs/12kebs/1http://amonline.trb.org/12kebs/12kebs/1http://safety.fhwa.dot.gov/roadway_dept/night_visib/retrotoolkit/index.htmhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/retrotoolkit/index.htmhttp://safety.fhwa.dot.gov/roadway_dept/night_visib/retrotoolkit/index.htmhttp://amonline.trb.org/12kebs/12kebs/1http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/TRB-130033.pdf


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APPENDIX A

THE POLICY ISSUE


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The following section summarizes the process local agencies can use to establish a signmanagement approach.

The FederalManual on Uniform Traffic Control Devices (MUTCD)and the Minnesota version(MN MUTCD) contain a requirement that all highway agencies must adopt a method of traffic

sign maintenance by June 13, 2014 [14]. Since there is no enforcement mechanism for this newrequirement, it is incumbent on the staff at each agency to take the necessary steps to achievecompliance. Being consistent with the requirements contained in theMUTCDis an importantpart of each agencies best practices efforts to manage both their system of traffic signs and theirrisk because theMN MUTCDhas been officially adopted for use on all public roadways inMinnesota and because the document is considered to be a standard against which an agenciesactions will be compared if allegations of negligence arise.

A review of Minnesotas tort law indicates that local agencies should consider two provenmethods. In order for agencies to bring their actions, relative to traffic sign maintenance, underan umbrella of immunity: Discretionary Immunity that is policy driven and Official Immunity

that is generated through the exercise and documentation of engineering judgment.

A.1 Policy Discussion

Pursuant to Minn. Stat. 466.03, Subd. 6, a city is immune from liability for: any claim basedupon the performance or failure to exercise or perform a discretionary function or duty whether

or not the discretion is abused. As a practical matter, the more it looks like discretion wasabused the more likely a court may determine that discretion was not exercised.Discretionaryimmunity exists because the government must make decisions. It must make decisions on how tobest spend taxpayers money and to prioritize the use of limited financial, personnel and otherresources. In addition, there are frequently competing policy considerations concerning what acity should do. Discretionary immunity recognizes that difficult decisions sometimes need to bemade. Discretionary immunity should apply when a government decision involves the weighingof competing political, social, economic or safety factors.

Discretionary immunity is policy driven actions that are consistent with adopted writtenpolicies and ordinances are considered as a matter of law to be immune from allegations ofnegligence. Therefore, it is considered to be a best (risk management) practice to have anagencys decision regarding the adoption of a traffic sign maintenance method included in apolicy or resolution enacted by the highest governmental decision making body (city council,county board, township board) following a discussion and consideration of the technical detailsof your system of signs, your maintenance capabilities and non-technical issues including social,economic, environmental and political considerations. In addition to the topic of traffic signmaintenance methods, it is considered a best practice to also include a discussion andconsideration of a number of related signing topics. The topics and a brief description for eachare provided in the following paragraphs.

A.1.1 Sign Maintenance Methods

There are three documented traffic sign maintenance methods; Assessment methods,Management methods and a Combination of methods [15]. The Assessment methods arebasically quantitative and involve having trained inspectors drive the agencys highway


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system, observing each sign and assessing the observed or measured level ofretroreflectivity. The Management methods are basically qualitative and are primarilybased on the expected life of the signs sheeting material. The Combination of methodswould employ elements of both the quantitative and qualitative approaches to signmaintenance.

A.1.1.1 Assessment MethodsAssessment methods require trained inspectors to conduct an in-field review of everysign in an agencys system. The Visual Nighttime assessment is conducted duringperiods of darkness, at normal speeds from the travel lane, using low-beam headlightsand at typical viewing distances based on 30 feet of legibility distance per inch of letterheight (180 feet for street name blades with 6-inch letters, 300 feet for STOP signs with10-inch letters and up to 1,100 feet for symbol type warning signs). FHWA guidancesuggests that one of the following procedures should be used to support the visualnighttime inspections:

1.)

Calibration Signs This procedure involves an inspector viewing a calibrationsign prior to conducting each nighttime field review. The calibration signs wouldhave known levels of retroreflectivity, preferably just above the minimumthreshold for a particular color and type of sheeting material. The calibrationsigns would be set up in a maintenance yard where the inspector could view thesigns in a similar manner to the nighttime field inspections. The inspector wouldthen use the visual appearance of the calibration sign to establish the evaluationthreshold for that nights field inspections.

2.) Comparison Panels This procedure involves assembling a set of comparisonpanels that represent retroreflectivity levels just above the specified minimums.Inspectors would then conduct the nighttime field review and when a marginalsign is observed, a comparison panel would be temporarily attached and thesign/panel combination viewed. Any signs found to be less bright than the panelwould then be scheduled for replacement.

3.) Consistent Parameters The nighttime inspections would be conducted undersimilar factors (vehicle and human) that were used in the original research toestablish the minimum retroreflectivity thresholds. These factors include; using ayear 2000 or newer Sport Utility Vehicle or Pick-Up truck (similar type andheight of head lamps) and using an inspector at least 60 years of age with 20/20vision (corrected).

An alternative Assessment method involves measuring the retroreflectivity of every signin an agencys system with a calibrated retroreflectometer (approximate purchase price =$10,000). The results from multiple readings of each color are averaged and recordedand the results are compared to the minimum threshold levels. Signs with actualretroreflectivity levels below the adopted minimums would be scheduled for replacement.


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A.1.1.2 Management MethodsThe Management method is qualitative, does not involve in-the-field inspections and isfundamentally based on estimating the expected life of signs using the manufacturerswarranty, research or the performance of a small set of control signs. The Expected SignLife and the Blanket Replacement methods are similar from the perspective that an

agency would adopt an expected sign life for their inventory based on an understandingof the sheeting materials warranty, prevailing weather conditions and levels of vandalism(for example, if signs need to be replaced every few years because they are being shot,selecting an expected sign life would probably not be a good strategy). Then all of thesigns in the inventory that are older than the expected life along a specific route, corridoror in an area are blanket replaced at one time. An example of using expected sign lifeto drive a sign maintenance program involves MnDOTs adoption of 15 years as theexpected life of their inventory of signs and then scheduling replacement of 1/15 of allthe signs in each of their Districts on an annual basis.

The Management method also includes a technique that uses a small set of control signs

(all of the basic colors oriented in the most adverse direction) that, for convenience andsafety, could be located in a maintenance yard. These control signs would be set upsimilar to signs installed along the highway system and then monitored to determinewhen the retroreflectivity drops below the established minimum thresholds. All of the in-the-field signs represented by the control sample would then be replaced just before thecontrol samples reach the minimum specified levels. New signs would periodically beadded to the control sample when signs are upgraded in-the-field.

A.1.1.3 Combination of MethodsThe Combination of methods would describe a process that includes elements of both theAssessment and Management methods. An example would be combining thereplacement of signs based on the expected sign life and conducting annual nighttimeinspections to find the few signs that might be outliers or that have the kind of damagethat is only visible at night (i.e., damage from paint balls).

Determining which method is best for a particular agency would involve consideration ofthe probable costs and benefits. The Assessment methods require training staff and manystaff hours conducting the annual nighttime field inspections. For example, its estimatedthat to observe all of the signs along a typical county highway system (10,000 signs)would require approximately 500 hours, or one-quarter of a full time employee operatingafter normal business hours. The primary advantage of using an Assessment method isthat agencies will likely get the most possible years of service from each sign in theinventory. On the other hand, the Management methods require less staff time sincethere are no in-the-field inspections, but it is also probable that some signs in theinventory will be replaced when they have some life remaining. If the issue of replacingsigns with some remaining life is considered critical, an agency could salvage the signsbeing removed based on reaching the expected life, measure the retroreflectivity in theshop, and retain those still meeting specifications as potential replacements for signsdamaged by vandalism or knockdowns.


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There is no uniform best practice for selecting a method of maintaining an agencyssystem of traffic signs, because the characteristics of each agencys system assets and thenumber and composition of the staff and other resources are different. However, FHWAsuggest that agencies consider three factors. The first is the size of an agencys signinventory. If the number of signs in the inventory is relatively small (fewer than 500),

conducting annual inspections would be fairly easy and not too time consuming. If thenumber of signs in the inventory is large (more than 5,000), conducting the annualinspection could require hundreds of staff hours and suggests consideration of one of theManagement methods. The second factor involves an agencys professional staff. If theprofessional staff are trained and have experience conducting nighttime inspections, itwould be easy to continue. If an agency does not have trained staff, the choices wouldinclude adding staff and training them or adopting one of the Management methods. Thethird factor involves the willingness to purchase measurement devices. If an agencyalready owns or is willing to purchase a retroreflectometer or a kit with samples ofsheeting material at the thresholds (a kit is currently under development at MnDOT StateAid or Avery Dennisonhas a kit available for purchase), one of the Assessment

methods may be best. If an agency chooses not to make these investments, the VisualAssessment or one of the Management methods would be a better choice.

One final point regarding the adoption of a sign maintenance method it doesnt have tobe permanent weigh the various factors, understand the characteristics of the systemand staff, make a decision and move forward and then re-evaluate periodically.

A.1.2 Best Practice Statements for Sign Maintenance Policy

A.1.2.1 Sign Maintenance Policy Best PracticeTheMN MUTCDrequires agencies that manage systems of traffic signs to adopt a

method for maintaining minimum levels of retro-reflectivity. The optional methodsavailable for use have been previously described and include either some manner of

annual visual inspection of each sign in the system by trained inspectors or a system

approach based on the expected life of the reflective sheeting material used by the

agency. In Minnesota, a suggested best practice approach involves documenting an

agencys decision to adopt a particular sign maintenance method in a policy enacted by

the agencies elected officials. This approach is based on Minnesotas tort law that

provides for discretionary immunity (from claims of negligence) for policy driven

actions, such as sign maintenance.

A best practices statement suitable for inclusion in a sign maintenance policy would be:

The ______________ County Highway Department/the City of ______________ Public WorksDepartment will conduct one nighttime inspection per year on its system of roadways and willuse the Blanket replacement method to maintain traffic sign retroreflectivity.


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A.1.2.2 Type of Reflective Sheeting Material Best PracticeDecisions regarding the type of sheeting material to use across a system of roadwaysusually come down to three factors; performance, cost (including expected life/life cyclecosts) and the extent to which an agencys signs are vandalized.

The newer, higher grade prismatic sheeting materials (ASTM Type IX & Type XI) aresignificantly brighter and have probable life expectancies in the range of two to fourtimes longer than the older beaded materials (ASTM Type I, Type IV). However, theinitial cost of the prismatic sheeting is three to four times higher than the cost of thebeaded sheeting. Due to longer life expectancies, the life cycle costs of the prismaticsheeting could be as much as 50 percent below the costs for the beaded sheeting (signlasts longer based on retroreflectivity and replacement is needed less often).

It should also be noted that because the cost of the reflective sheeting material makes uponly a part of the installation costs, the total cost of installing a traffic sign (sign blank +sheeting + posts + labor) actually falls in a fairly narrow range and that suggests that

agencies would likely pay a premium of between 5 and 15 percent for the initialinstallation of the higher performance sheeting when all components are taken intoaccount and little effect over the entire sign life cycle.

Finally, if many of an agencys signs are being vandalized such that virtually none of thesigns actually approaches the expected sign life, the use of the longer lived/higherperformance material would likely not be a cost effective strategy.

A best practices statement would be:

The ______________ County Highway Department/the City of _______________ PublicWorks Department will use ASTM Type XI sheeting material for all traffic signs.

A.1.2.3 Citation of Expected Sign Life Best PracticeThe dilemma for agencies in the selection of an expected sign life stems from the fact thatit cannot be said with a high degree of certainty at this time what the expected life is for aparticular sheeting material on a particular sign. Not enough data has been collected, notenough analysis has been completed and not enough research published. What is knownis the warranty period provided by manufacturers (7 to 10 years for beaded material and12 years for prismatic). However, there is an expectation that the actual life of a sign isconsiderably longer based on observations of agency staff and there is some preliminaryevidence that supports this notion. A survey of other state DOTs found that four of thefive states interviewed adopted sign lives in the range of 15 to 20 years [16]. In addition,the readings of retroreflectivity documented as part of this project suggest a reasonablelife expectancy is beyond the warranty period and would likely be in the range adoptedby a number of other state DOTs in the range of 10 to 20 years for beaded sheeting and15 to 30 years for prismatic sheeting.


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The _______________ County Highway Department/the City of _______________ PublicWorks Department adopts a sign life of 15 years for all signs in our inventory.

A.1.2.4 Damaged Sign Replacement Best PracticeIt is important for agencies to establish reasonable time frames for their crews to repairdamaged signs following receipt of a notice that a sign has been damaged. It is alsoimportant for agencies to acknowledge that all signs are not equally important for thesafety of motorists, therefore, response times for the repairs should vary based on theassumed importance of the sign. There appears to be agreement that replacing damagedSTOP signs should have the highest priority because of the concern for severe crashes ifthe STOP sign is not visible. A reasonable approach to addressing damaged STOP signswould be repair/replacement within one business day of notification. There also appearsto be agreement about lower priority signs, generally Guide signs and street name signs.A reasonable approach to addressing damaged Guide signs would be repair/replacement

within three business days (an agency may determine and change the timeframe based onweighing political, social, economic and safety factors). There was not generalagreement based on sample policies on which types of signs belonged in the intermediatecategory. One agencys policy identified this intermediate category as being not directlyvital for safety, such as speed limit and most warning signs. Another agency identifiedthe entire category of Warning signs as the intermediate priority. A third possibilitycould identify all of the Regulatory, Warning and Guide signs that are a SHALLdescription for installation in theMN MUTCD. This group of signs would include; SpeedLimit signs (for established speed zones), ONE WAY /DO NOT ENTER, TurnProhibitions, All-Way STOP Plaque, Advanced Rail Road Crossing, Bridge Clearance &Weight Limits, Horizontal Alignment series (Average Daily Traffic based), RouteNumbers, Junction Assembly and the Advanced Turn Assembly.


The _______________ County Highway Department/the City of _______________ PublicWorks Department will repair/replace signs after receipt of notice that a sign has been damagedbased on the following schedule:

High Priority Signs (STOP signs) within one business day

Intermediate Priority Signs (Reg., Warning and Guide Signs required by the MNMUTCD) within 2 scheduled business days

Lower Priority Signs (All other Regulatory, Warning & Guide signs) within 3

scheduled business days

A.1.2.5 Signs Requested to be Installed on Agencys Right-of-Way Best PracticeExperiences shared by county and city engineers suggest that agencies will at some timebe asked by the public to investigate a segment of roadway or an intersection because of aperceived safety problem, for which the publics suggested solution is to install aparticular traffic sign. If the agencys investigation concludes there is not a problem andno signing change that would make the situation better, the publics response in some


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cases is to offer to pay for installing the requested sign themselves. It appears that therequestor attributes the conclusion to not install their suggested sign because of the costas opposed to any consideration of effectiveness. In order to be responsive to the public,agencies are required to provide an explanation for their decision and there are twoprimary approaches to crafting this response. First, the agency can explain the technical

reasons for their decision, including; documenting the data they collected, the results ofthe analysis that was completed, determination as to whether the documented conditionswere different than what would be expected and finally explaining that the decision to notinstall a sign was based on either not finding a real problem or a conclusion that no signwould be effective at achieving the publics desired outcome. More often than not, thistype of technical explanation fails to be persuasive with the public; it is counter-intuitiveplus they may have seen a sign installed in a similar situation in another jurisdiction. Thesecond and more effective strategy is to refer to a policy adopted by the county board/citycouncil that says that all signs requested to be placed in the right-of-way of the countyroadway/city street must meet the requirements of theMN MUTCDAND have theapproval of the county engineer/city engineer. These provisions should be sufficient to

prevent the installation of virtually all unusual signs (i.e., SLOW CHILDREN,CHILDREN AT PLAY, etc.) which have never proven to be effective at improvingsafety but will increase an agencys maintenance costs and increase an agencys risks ifthey are not c

mndot traffic sign life expectancy report

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